Tennis string



'No Drawing.

Patented July 15, 1 930 UNITED STATES PATENT, oFFicE GUSTAVE s. marnnmorELIZABETH, NEW JERSEY, ASSIGNOR T0 JOHNSON & :ronnson, or NEW BRUNSWICK,NEW JERSEY, A conronnrrou on NEW JERSEY TENNIS STRING and disadvantagesof steel strings'are similar to those of silk. Vhether covered or not,

steel strings are less lively than gut and steel strung rackets have adifierent feel.

There are on the market at present only a few synthetic strings. Braidedstrings are rapidly disappearing. A few special strings, combining gutand silk, have been offered, but their disadvantages over-shadow anyapparent advantages.

The silk string offers the best solution provided it can be improved asto resiliency and as to waterproof properties.

After extended experimentation with many raw materials and diversmethods of fabrication and treatment, I have devised a comparatively lowcost strand which practically equals the resiliency of gut and fordurability and over all efficiency is far superior to gut. It possessesthe further merit that in appearance it is almost identical with gut inthat it is substantially transparent, a

cross-section of the string revealing nofibrous structure. And the newstrand may he untwisted with even more difiiculty than is the case withgut strings.

In-the practice of m invention, '1 start with silk in the boiled-ocondition, i. e. free from the silk gum, ceresin. of ceresin is highlyimportant for I have found that the presence of this substance is 'adeterrent to successful impregnation and accounts for past failures. Asize of silk which has proven satisfactory is 22 thread 13/15 Japantram.

Having, as stated, completely removed all traces of ceresin, the strandsof silk are twisted and drawn under desirable tension through anappropriate glue mixture which is held at a carefully regulatedtemperature.

The elimination Application filed July 9, 1927. Serial No. 204,667.

In general, the higher the temperature, the better the impregnation.However, it is not desirable to raise the temperature of the glueappreciably beyond 7 0 (1., otherwise hydrolysis of the glue takes placeand the finishedstring is likely to be decidedly brittle. Thetemperature is regulatedaccording to the fluidity of the glue and theappearance of the twisted string.

As a result of testing a number of types of cementing agents such asglass, resins, varnishes, lacquers, etc., I have found that a truecolloid in solid form to the jelly form results in a true colloid jellywhich shrinks uniformly and dries without any. separation from thestrands. I

Inthose tests in which varnishes or lacquers were used, it was foundthat the resulting strings were quite large, poorly impregnated, slow indrying, and not at all satisfactoryas tennis strings.

F lexibilityinthe finished string is essential, otherwise the stringwill almost certainly break at the frame in the stringing process. Thedesired flexibility may be obtained by the use of a satisfactorysoftening agent in the glue mixture. However, the use of such agent inthe required amount tends to confer uponthe string a resin-like surfaceso that when the string is pulled through a racket form it. slips atintervals as though it were treated with pine resin. Obviously, thiscondition is altogether undesirable inasmuch as it makes fornon-uniformity of tension. To overcome this action of the softeningagent, I add a good lubricant such as castor oil, lard or othervegetable or animal product; Good results have also been had withpetroleum oils. The oil is stirred into the glue mixture until a uniformemulsion is formed "in which no trace of oil may be observed. Such anemulsion may be kept almost indefinitely with no separation into itscomponents and glycol, triethylene glycol, the various p satisfactoryproducts are given in the accompanying table,

It will be noted. that the compositionpf the glue mixture or emulsionmay bevaried over rather wide limits according to the characteristicsdesired in the product. Other softening agents such ,as glycol,diethyleine glycerins, etc'., may be substituted for the glycerin usedin the present process, and various oils of almost any stituted for thelard.

The properties of the finished pendlargely upon its structure. stringhaving from two to four twists to the inch, and referably a twist ofthree turns to the inch, as proven eminently satisfactbry. A stringcontaining glue as: such is not waterproof. By vproper treatment,however, the glue may be rendered very resistant to the action ofmoisture. The common tanning agents for leather are in general capableof rendering glue moisture-proof. Amon these are formaldehyde, otheraldehydes, hexamethylene tetramine, tannic acid, potassium dichromate,and chromium and aluminum salts. .From the standpoint of ease ofhandling, low price and results obtained, formaldehyde has been mostsatisfactory. As carried out at present, curing is obtained orlgin maybe substring de- A twisted by exposing the twisted string to the vaporof formaldehyde in a closed environment.

e use of solutions of formaldehyde containing the softening agent usedin the glue mixture has also proved satisfactory.

After removal from the curing vessel the strings are stretched tightlyand allowed to remain until dry. The quality of the strings is improvedsomewhat if the drying is conducted under considerable tension.

After the strings are thoroughly dried, any small surface irregularitiesmay be removed by polishing with lard or other oil.

A satisfactory string must possess a breakuse of between fifty or sixtystrands of 22 thread 13/15 Japan tram.

sand paper or equivalent, whereupon the strings are wiped off with wellqualified or may readily be qualified for other purposes by modifyingthe glue bath, by proper choice of caplllary bore or other trim, and/orby varying the number of strands. For example it maysreplace raw hide inhookless belt lacing.

Having described my invention, I clann:

synthetic gut, comprising tw sted strands of degummed silk, and anemulsified colloidal bond having lubricating and water-proofingproperties.

In testimony whereof I afiix my signature.

GUSTAVE S.MATHEY.

Strings ofa solid color may be providedby simply adding the emulsion orglue mixture. Where more than one color is required, the use .of two ormore kinds of colored silk will insure the desired combination ofcolors.

While the present tended for use as a desired color to the product ismainly in substitute for gut itis

